The generation and use of chlorine dioxide for disinfection purposes, bleaching, and related oxidative tasks, has been disclosed in the technical literature as well as in an extensive series of patents. In general, for large scale usage, chlorine dioxide has been directly created by oxidation or acidification of chlorite, and/or by reduction of chlorate. When chlorite is acidified, the resulting chlorous acid (hydrogen chlorite) is an unstable species that decomposes to form the higher-valent chlorine dioxide gas and chlorate, and the lower-valent chloride ion. At lower concentrations of either or both reactants, the transformation is much less rapid. Thus, commercial production of chlorine dioxide gas is generally effected with higher reactant levels.
There have been many unique approaches to the generation of chlorine dioxide under specialized circumstances. Examples of these can be found in U.S. Pat. No. 4,104,190 wherein chlorite is oxidized by a chlorine source; in U.S. Pat. Nos. 4,689,169 and 5,399,288 wherein chlorine dioxide is generated from dry compositions; in U.S. Pat. Nos. 4,731,193 and 4,861,514 wherein chlorine dioxide is generated in thickened media for extended activity; and in U.S. Pat. Nos. 5,104,660 and 5,126,070 wherein chlorine dioxide is created by rupture or addition of moisture to dry precursors in enclosed compartments. Other approaches for generating chlorine dioxide include formation from concentrated reactants as disclosed in U.S. Pat. Nos. 3,386,915 and 4,925,645 and Canadian Patent No. 959,258; triggering chlorite with transition elements as disclosed in U.S. Pat. No. 5,008,096; and interaction of adsorbed precursors impregnated into zeolites as disclosed in U.S. Pat. Nos. 5,567,405 and 5,573,743. Additional means of providing chlorine dioxide, such as disclosed in U.S. Pat. Nos. 3,123,521 and 3,271,242, are by acidification or dilution of so-called "stabilized chlorine dioxide solutions." Such solutions, however, are in reality stabilized chlorite solutions, since small amounts of chlorine dioxide that are slowly created in chlorite solutions are continuously reduced back to the chlorite form by peroxy compounds.
Other disclosures have dealt with the use of chlorine dioxide for specific disinfection purposes. These include U.S. Pat. No. 4,021,585 disclosing a low-concentration chlorine dioxide spray for meat disinfection; U.S. Pat. No. 4,504,442 teaching the use of chlorine dioxide gas to disinfect impermeable surfaces; U.S. Pat. No. 5,116,620 for disinfecting wounds; and U.S. Pat. Nos. 5,152,912 and 5,279,673 for disinfecting contact lenses. Chlorine dioxide was also one of several means used to disinfect fish, as part of a patented sequential process for preserving its quality, which involves disinfection, supercooling, and sub-zero, non-frozen storage of the fish, as disclosed in U.S. Pat. No. 4,832,972.
Bacterial attack on fresh food items of commerce has long been a problem. Between the time of harvesting agricultural commodities, or catching fish and/or shellfish on ocean-going vessels, or transporting freshly-killed poultry, and the like, and/or retail storage of these food materials, and the customer's purchase of these foods, pathogenic and spoilage bacteria continue to multiply exponentially. Cooler temperatures tend to suppress this growth. In many operations ice and refrigeration have been used to retard such spoilage, as was disclosed in the process described for extending the shelf life of fish in U.S. Pat. No. 4,832,972. In addition, many freshly-collected food items can be subjected to initial disinfecting sprays, such as with chlorinated water, sorbates or organic acids.
A recent Food Additive Petition has been made to the U.S. Food & Drug Administration, in which the commercial use of ice containing chlorine dioxide has been requested (Bio-Cide International, Inc., Food Additive Petition 6A4499, filed May 8, 1996). The preparation of such ice is somewhat tedious, and potentially dangerous with respect to the inhalation of high levels of chlorine dioxide from the initial concentrates. These concentrates are prepared, for example, from a combination of 10% citric acid and 2.0% aqueous sodium chlorite solution, which results in upwards of 5,000 parts per million (ppm) of chlorine dioxide in the solution. The solution is then diluted with water so that the final concentration of chlorine dioxide plus sodium chlorite is no more than about 25 ppm, which liquid is then frozen. Since the permitted level for continuous exposure of factory workers to chlorine dioxide is only 0.1 ppm in the air, and since chlorine dioxide is a volatile gas, such preparation and use is potentially problematic, as well as expensive.
However, one of the advantages of chlorine dioxide is that, as a gas, it can escape from frozen or re-liquefied water and permeate the surfaces of food to reduce their microbial loading. To this end, the use of chlorine dioxide-impregnated ice would be particularly advantageous for the storage of fish and shellfish after harvesting. Fish, particularly in tropical areas, can spoil within hours at ambient temperatures because bacteria on their surfaces multiply rapidly and invade the tissues. The putrefaction that results from such proliferation, as well as degradative biochemical processes, could well be suppressed by the use of ice containing chlorine dioxide. However, the large quantities of ice that would be needed would be prohibitively expensive if prepared by the activation/dilution process that is currently under development.
Accordingly, there is a need in the art for simpler and more cost-efficient techniques for producing chlorine dioxide-containing ice, as well as the use of such ice to disinfect a variety of substrates, particularly food. The present invention fulfills these needs, and provides other related advantages.